Key Engineering Materials Vols. 336-338

Abstract: This paper studied the dielectric performances and microstructure of the Ba-Ti-B-Si-O glass-ceramics fabricated with different methods. The experimental results showed that the pre-calcined method was an effective way to decrease the sintering temperature in glass-ceramic fabricating process, and the dielectric properties of the LTCC materials were εr ≈10, tanδ ≤ 2×10-3 (@1MHz). This study provided a composite method to fabricate LTCC for different applications that was composed of pre-calcined powders and molten powders with different ratios; Moreover, the dielectric constant and sintering performance of composite LTCC were adjustable by changing the ratio of pre-calcined powders and molten powders.

Abstract: The effect of Fe2O3-TiO2 mixture additives on the crystallization behaviour of a parent glass with composition located in the primary field of cordierite within the MgO-Al2O3-SiO2 system has been examined. The crystallization behaviour of the glass was determined by differential thermal analysis (DTA) and X-ray diffraction (XRD). The microstructure was characterized by scanning electron microscopy (SEM). The results show that additives of Fe2O3-TiO2 can lower the temperature of the crystallization peak (Tp) and promote crystallization of the parent glass. By controlled thermal treatment, the main crystal phase obtained was Fe2+
substituted α-cordierite. The approach outlined in this paper to obtain heterogeneous ion substituted cordierite
glass-ceramics is useful to develop infrared radiation material with good properties.

Abstract: The effects of Li+ addition on the sintering and microstructural evolution of cordierite were analyzed. As nucleating agent, the Li+ additive decreased the expansion coefficient and dielectric constant. The doping of Li+ was found to block the phase transition from μ-cordierite to α-cordierite and increase sintering temperatures. The effect of Li+ on the activation of cordierite can be attributed to the nucleation of cordierite. Too much Li+ will inhibit the cordierite crystallization and encourage amblygonite crystallization. Cordierite powders were prepared by sol-gel processing.

Abstract: In this paper the Li+, Sb3+-doped SiO2-TiO2 thin films, which were heat-treated with an applied electric field, were prepared by sol-gel dip coating. The crystallization of the thin films in the electric field heating-treatment was studied by X-ray diffraction (XRD) and atomic force microscope (AFM). The photo-catalytic activity of SiO2-TiO2 films was studied under the condition of an electric field heating-treatment and mixing with some additive such as Li+ and Sb3+. Finally, studies on photo-catalytic degradation showed that the Li+, Sb3+-doped SiO2-TiO2 films on the quartz glass, of high photo-catalytic activity, were successfully obtained in the electric field heating-treatment.

Abstract: 5~15 wt% MgO-CaO-Al2O3-SiO2 (MCAS, fabricated by sol-gel method) glass is used as the sintering aid of AlN ceramics. The sintering is proceeded from 1350oC~1550oC, scanning electron microscope is used to observe the sintered morphologies and X-ray diffraction pattern are used to confirm the crystal structures. From the SEM observations, as 10wt% and 15wt% MCAS is added, AlN ceramics can be densified at 1500oC and 1450oC, which are much lower than the before studies were. From the X-ray diffraction patterns, the crystal phases of MCAS-AlN ceramics are AlN, Al2O3, and cordierite phases. In this study, the dielectric characteristics of MCAS-AlN ceramics are also developed as a function of MCAS content and sintering temperature.

Abstract: Glass ceramic was successfully synthesized using goldmine tailings as main raw material. The frit preparation and molding techniques, and the nucleation and crystallization processes were discussed. The results showed that only one crystalline phase, idiomorphic diopside, was formed in shapes of small columns and grains. The optimum temperatures for melt, sintering, nucleation and crystallization were 1350°C, 1160°C,
750°C,
and 860°C, respectively.

Abstract: A method is proposed for estimating the critical cooling rate for glass formation and continuous cooling transformation curve (CCT) from isothermal TTT data. The critical cooling rates and CCT curves for a group of lithium disilicate glasses containing different amount of Pt as nucleating agent estimated through this method are compared with the experimentally measured values and it shows this method can give a reasonable estimation.

Abstract: Biomorphic SiC ceramics were fabricated by infiltrating liquid silicon into woodceramics which were prepared from beech and pine impregnated with phenolic resin (PR) of different viscosity in order to reinforce the cell wall of wood. The viscosity of phenolic resin was adjusted by ethanol according to the weight ratio of PR to ethanol. The samples not impregnated with resin were compared. Effect of viscosity of phenolic resin on the dimension shrinkage, weight loss, porosity and the axial and radial flexural strength were investigated. Microstructural observation and phase identification of woodceramics and biomorphic SiC were performed by SEM and XRD, respectively. The results show that, the lower the viscosity of phenolic resin was, the higher the dimension shrinkage, weight loss and porosity of woodceramics were. Biomorphic SiC was a diphase composite consisting of major phase β-SiC and secondary phase Si. Woodceramics made from pine swelled or broke and strength of woodceramics fabricated from beech declined when higher viscosity resins were impregnated. The flexural strength of biomorphic SiC increased with increasing in viscosity of PR. The axial flexural strength was significantly higher than the radial flexural strength because of anisotropic pore microstructures.